Process for making pulp by impregnating cellulosic materials with ammonium hydroxide and nitric acid



United States Patent PROCESS FOR MAKING PULP BY IMPREGNAT- IN G CELLULOSIC MATERIALS WITH AlWMO- NIUM HYDROXIDE AND NITRIC ACID Everett C. Mills, Seattle, Wash., assignor, by mesne assignments, to Alscope Limited, Passaic, NJ., a corporation of Delaware N0 Drawing. Continuation-impart of application Ser. No. 410,727, Nov. 12, 1964. This application Feb. 1, 1968, Ser. No. 703,541

Int. Cl. D21c 3/16 U.S. Cl. 162-451 4 Claims ABSTRACT OF THE DISCLOSURE A process for making pulp characterized by the step or steps of impregnating comminuted cellulose-containing material with an ammonium compound and an aqueous solution of nitric acid, either sequentially or concurrently, initiating an exothermic oxidation reaction between the lignins of said material and the nitric acid, and controlling the temperature of said material to not exceed about 97 C. until completion of the oxidation reaction.

This application is a continuation in part of my copending application, Ser. No. 410,727, filed Nov. 12, 1964, now abandoned.

This invention relates to a process for pulping cellulosecontaining material such as hard or soft woods, agricultural straws, vines, stalks and grasses. More particularly, the invention is a process for removing all or any lesser amount of the lignins and other constituents of such material from the cellulose to produce various grades of either high or low yield pulp.

Among the objects of the invention are the following: the employment of nitric acid in minimal amount to achieve the breakdown and/0r oxidation of the noncellulosic constituents of the wood or other raw material, either the employment of a reagent such as ammonium hydroxide in minimal amount in company with the nitric acid or the employment of a wetting agent such as ammonium hydroxide in preceding relation to the use of the nitric acid to both expedite the breakdown and/ or oxidation step and to conserve the nitric acid against both direct loss and indirect, or degenerative, loss; and to obtain pulp in such short time and under such process conditions as to time, temperatures, pressures, and amounts of reactants handled and employed as to minimize the expense of pulp production.

One embodiment of the process, which may be carried out on a batch or continuous basis, involves the following steps or their equivalents:

A-The removal of moisture from the raw material, preferably by flushing the raw material, in chip or other comminuted form, with live steam;

B-Contacting the chips with the reactant liquor, an aqueous solution of nitric acid and ammonium hydroxide, in sufficient amount to impregnate the chips;

CSeparating the chips and the excess reactant liquor;

D-Initiating the exothermic oxidation reaction between the lignins and the nitric acid which impregnates the chips, as by subjecting the chips to steam; and

E-Controlling the temperature of the chips to not exceed about 97 C. until the completion of the oxidation reaction while removing from the situs of the chips any gaseous products evolved during the course of the reaction.

Thereafter, the chip material may be hot-washed, steamsoftened, caustic-cooked under pressure or not under pressure, cleared of any remaining nitric acid and other chemicals used in the process, final-washed, and beaten or screened, all in general accordance with conventional practices.

The reactant liquor referred to in step B comprises an aqueous solution of nitric acid of about 3 to about 18 B. and ammonium hydroxide in a concentration of approximately one part by weight to about 100250 parts by Weight of HNO The reactant liquor is preferably heated to about 50 C. before being brought into contact with the chips.

Step C may be carried out, for example, by evacuating the liquor on the outside of the chips and by subjecting the chips to a gas pressure on the order of 25 psi. to express excess liquor from within the chips.

The following examples provide data illustrative of the practice of the process of the invention. Pulp of a satisfactory to a very high quality grade was obtained as a result of each of the following process runs.

Example 1 (Redwood) Weight of chips gr 607 Moisture content of chips percent 12 Acid strength (15% of 42 B.). NH OHznitric acid (1 partzl00 parts). Vacuum (28 in.) min 8 Impregnation time min 10 Reaction temperature held at 97 -C min 30 Loss of nitric acid in chips after impregnation (vol.) ml 1,000 Caustic cook (NaOH conc.) "percent" 6 Cooking time at pressure of 20 lbs min Beating time min 15 Example 2 (Redwood) Weight of chips gr 1,140 Moisture content of chips percent 36 Acid strength (15% of 42 B.). NH OHznitric acid (1 partz parts). Vacuum (28 in.) .min 10 Impregnation time min 15 Reaction temperature held at 97 C min 45 Loss of nitric acid in chips after impregnation percent 11 Caustic cook (NaOI-I conc.) do 7 Cooking time at pressure of 20 lbs min 100 After-cook rinse (hot water) min 15 Beating time min 15 Example 3 (Rice straw) Weight lb 1 Moisture content percent 6 Acid strength 15% of 42 B.). NH OH:nitric acid (1 partz100 parts). Vacuum (28 in.). Impregnation time min 1f Loss of nitric acid in chips ml 1,000 Reaction time min 15 Reaction temperature C 9E Hot water wash before caustic cook None Caustic cook None Beating time min 2 3 Example 4 (Wheat straw) Weight of straw gr 1,000 Moisture in straw Not determined Acid strength (12% of 42 B.)

NH OH:nitric acid (1 part: 100 parts). Vacuum None Impregnation time min 8 Reaction time min 35 Reaction temperature C 94 Caustic cook (NaOH conc.) percent 5 Cooking time min Beating time min 5 Example 5 (Sudan grass) Weight of grass gr 650 Moisture of grass Not determined Acid strength (12% of 42 B.). NH OH:nitric acid (1 part: 100 parts). Vacuum None Impregnation time min 8 Reaction time min 30 Reaction temperature C 94 Caustic cook (NaOH conc.) percent 3 Cooking time min 10 Beating time min 5 Example 6 (Red fir) Weight of fir chips gr 950 Moisture in chips percent 30 Acid strength (13.5% of 42 B.). NH OH:nitric acid (1 part: 100 parts). Vacuum (28) in. min 10 Impregnation time min 12 Reaction time min 65 Reaction temperature C 96 Caustic cook (NaOH conc.) percent 6 Cooking time min 40 Beating time min 10 Example 7 (Bagasse) Weight of bagasse gr 730 Moisture in bagasse Not determined Acid strength (13% of 42 B.). NH OH:nitric acid (1 part: 100 parts). Vacuum None Impregnation time min 8 Reaction time min 40 Reaction temperature C 94 Caustic cook (NaOH conc.) percent 5 Cooking time min 20 Beating time min 10 Example 8 (Alder) Weight of chips gr 875 Moisture in chips percent Acid strength (12% of 42 B.). NH oHznitric acid (1 part: 100 parts). Vacuum (28 in.) min 10 Impregnation time min 12 Reaction time min 35 Reaction temperature C 94 Caustic cook (NaOH conc.) percent 5 Cooking time min 25 Beating time min 12 Example 9 (Pine) Weight of chips gr 1020 Moisture in chips percent 25 Acid strength (13.5% of 42 B.). NH OHznitric acid (1 part:100 parts). Vacuum (28 in.) min 10 impregnation time min 10 Reaction time min 70 Reaction temperature C 94 Caustic cook (NaOH conc.) percent" 5 Cooking time min 30 Beating time min 15 Acid strength 13.5% of 42 B.). NH OH:nitric acid (1 part: 100 parts). Vacuum (28 in.) min 7 Impregnation time min 12 Reaction time min 65 Reaction temperature C 96 Caustic cook (NaOH conc.) percent 13 Cooking time min 60 Example 11 (Aspen) Weight of chips lbs 100 Moisture in chips percent 50 Acid strength (15% of 42 B.). NH OHznitric acid (1 part: 100 parts). Vacuum (28 in.) min 5 Impregnation time min 13 Reaction time min 60 Reaction temperature C 96 Caustic cook (NaOH conc.) percent 5 Cooking time min 50 Cooking pressure p.s.i 10 Beating time min 15 Example 12 (Rice straw) Weight of straw lbs 20 Moisture in straw percent 10 Acid strength (3.5% of 42 B.). Vacuum (28 in.). Impregnation time min 10 Reaction time min 20 Reaction temperature C 96 Caustic cook (NaOH conc.) percent 2 Cooking time min 15 Cooking pressure p si 10 Beating time min 10 Example 13 (White spruce) Weight of chips lbs 110 Moisturein chips percent 50 Acid strength (15% of 42 B.). TW. of acid degrees NH OH:nitric acid (1 part: parts). Vacuum (28 in.). Impregnation time min 15 Reaction time min 60 Reaction temperature C..- 96 Caustic cook (NaOH conc.) percent 6 Cooking time min 70 Cooking pressure p si 10 Beating time min 20 A further and preferred embodiment of the process, which may be carried out on a batch or continuous basis, involves the following steps or their equivalents:

A-The impregnation of the raw material, in chip or other comminuted form, with ammonium hydroxide, or the equivalent thereof as a wetting or leaching agent for said raw material, followed by the expressing of the impregnant from said raw material;

B-Impregnating the raw material with an aqueous solution of nitric acid;

C-Separating the raw material and the excess nitric acid;

DInitiating the exothermic oxidation. reaction between the lignins and the nitric acid which impregnates the raw material, as by subjecting the latter to steam; and

E-Controlling the temperature of the raw material to not exceed about 97 C. until the completion of the oxidation reaction while removing from the situs of the raw material any gaseous products evolved during the course of the reaction.

This preferred embodiment of the process is particularly adavntageous for use where the raw material is a vegetable material.

Before subjecting the vegetable material to the action of ammonium hydroxide, the material is cut into small pieces approximately 1 inch in length. The material is then preferably steamed, thereby allowing for faster impregnation of the material by the ammonium hydroxide which serves to nitrate the lignins in the raw material.

The steamed raw material is then immersed into a hot (preferably within the range of about 4560 C.) solution of 8% ammonium hydroxide at atmospheric pressure. Time required to dis-incrust the raw material depends on whether it is a low or high density material, such time being usually within the range of about 30 to about 60 minutes. When the material has become impregnated with the ammonium hydroxide, it is subjected to a press, for example, to remove all of the excess ammonium hydroxide. The remaining ammonium hydroxide Within the raw material is approximately 2% by weight thereof.

The vegetable material is then impregnated with an aqueous solution of nitric acid having a concentration of from about 8% to about 20% of 44 Baume, the solution of nitric acid having been brought to a temperature of not in excess of about 45 C. The impregnation time is from about 8 to about minutes depending upon the density of the particular raw material being used. The impregnation time can of course be reduced if pressure is employed during this step. The vegetable material will absorb from about to about 32% by weight of the nitric acid solution depending upon the moisture content of the raw material.

The use of the ammonium hydroxide in the manner described results in a shorter reaction time for the subsequent oxidation reaction with nitric acid and enables a minimum usage of nitric acid from the standpoint of the amount required for the oxidation reaction. As a result of the oxidation reaction time being shortened and the decreased usage of nitric acid, pulp cannot only be produced at a lower cost per ton but with a lesser chance of hydrolysis occurring.

The loss of nitric acid solution due to such solution remaining in the vegetable material varies slightly with various raw materials, amounting to from about 20% to about 32% by weight of the vegetable material.

After the ammonium hydroxide is expressed from the vegetable material, the ammonium hydroxide remaining in this material acts as a wetting agent, thereby speeding up the rate of penetration of the nitric acid solution into the raw material.

Some examples of the preferred embodiment of the subject process are as follows:

Example 14 (Wheat straw) Weight of wheat straw gr 700 Moisture content of straw percent 1 Wheat straw steamed then immersed in hot solution of NH OH, 6% of 26 Baum min 30 All but approximately 2% of the NH OH then pressed from the wheat straw. Nitric acid aqueous solution brought to a temperature of 45 C. Straw impregnated with hot nitric solution of 12% of 42 min 10 Loss of nitric acid in impregnation ml 550 Reaction temperature held at 94 C min 30 Caustic cook (NaOH) percent 3 Cooking time at pressure of 20 lbs min 15 Beating time min 1 Hot water wash. Screen. Yield, approximately percent 37 6 Example 15 (Maize stalk) Weight of maize stalk gr.. 750 Moisture content of maize percent 2 Maize steamed then immersed in hot solution of NH OH, 8% of 26 Baum min- 35 All but approximately 2% of the NH OH then pressed from the maize stalk. Nitric acid aqueous solution brought to a temperature of 45 C. Maize impregnated with hot nitric solution of 15% of 42 Baum min 12 Loss of nitric acid in impregnation ml 600 Reaction temperature held at 96 C min 35 Caustic cook (NaOH) percent 4 Cooking time at pressure of 20 lbs. min 20 Beating time min 2 Hot water Wash. Screen. Yield (approximately) percent 35 Example 16 (Cotton stalk) Weight of cotton stalk gr 800 Moisture content of cotton stalk percent 2 Cotton stalk steamed then immersed in hot solution of NH OH, 5% of 26 Baum min 45 All but approximately 2% of the NH OH then pressed from the cotton stalk. Nitric acid aqueous solution brought to a temperature of 45 C. Cotton stalk impregnated with hot nitric solution of 15% of 42 Baum min-.. 12 Loss of nitric acid in impregnation ml 525 Reaction temperature held at 96 C min 35 Caustic cook (NaOH) percent 3 Cooking time at 20 lbs. pressure min 20 Beating time min 2 Hot water wash. Screen. Yield (approximately) percent 37 Example 17 (Maize stalk) Weight of maize gr 825 Moisture content of maize percent 2 Maize steamed then immersed in a hot solution of NI-I OH, 10% of 26 Baum min 60 All but approximately 2% of the NH OH then pressed from the maize stalk. Nitric acid aqueous solution brought to a temperature 45 C. Maize impregnated with hot nitric solution of 20% of 42 Baum min 15 Loss of nitric acid in impregnation ml 650 Reaction temperature held at C. min 40 Caustic cook (NaOH) percent 5 Cooking time at pressure of 20 lbs min 20 Beating time min 3 Hot water wash. Screen. Yield (approximately) percent 38 What is claimed is: 1. In the process for making pulp comprising cellulose from a raw material selected from the classes consisting of wood and vegetable matter in sub-divided form, the breaking down of lignins in the raw material by:

(A) presteaming the raw material to decrease the moisture content of the raw material to thereby increase the capacity of the raw material to become impregnated with an aqueous solution;

(B) impregnating the raw material with a dilute aqueous solution of nitric acid which also contains as a solute an amount of ammonium hydroxide, the ammonium hydroxide having a concentration of about one part by weight for about every 100250 parts by Weight of HNO present in said solution;

(C) removing the excess of said solution from the raw material;

(D) heating the raw material to initiate an exothermic reaction between the HNO impregnant of the raw material and lignins of the raw material; and

(E) controlling the temperature of the raw material during the reaction so that it does not exceed about 97 C.

2. In the process for making pulp comprising cellulose from a raw material selected from the classes consisting of wood and vegetable matter in sub-divided form, the breaking down of lignins in the raw material by:

(A) impregnating the raw material with a dilute aqueous solution of nitric acid which also contains as a solute an amount of ammonium hydroxide, the ammonium hydroxide having a concentration of about one part by weight for about every 100-250 parts by weight HNO present in said solution;

(B) removing the excess of said solution from the raw material;

(C) heating the raw material to initiate an exothermic reaction between the HNO impregnant of the raw material and lignins of the raw material; and

(D) controlling the temperature of the raw material during the reaction so that it does not exceed about 97 C.

3. In the process for making pulp comprising cellulose from a raw material selected from the classes consisting of wood and vegetable matter in sub-divided form, the breaking down of lignins in the raw material by:

(A) impregnating the raw material with a dilute aqueous solution of ammonium hydroxide and removing the excess of said ammonium hydroxide from said raw material;

(B) impregnating the raw material with a dilute aqueous solution of nitric acid and removing the excess of said nitric acid from said raw material;

(C) heating the raw material to initiate an exothermic reaction between the HNO impregnant of the raw material and lignins of the raw material; and then (D) controlling the temperature of the raw material during the reaction so that it does not exceed about 97 C.

4. In the process for making pulp comprising cellulose from a raw material selected from the classes consisting of Wood and vegetable matter in sub-divided form, the breaking down of lignins in the raw material by:

(A) impregnating the raw material with a dilute aqueous solution of ammonium hydroxide and removing the excess of said ammonium hydroxide from said raw material;

(B) impregnating the raw material with a dilute aqueous solution of nitric acid and removing the excess of said' nitric acid from said raw material;

(C) heating the raw material to initiate an exothermic reaction between the HNO impregnant of the raw material and lignins of the raw material, said solution of ammonium hydroxide having a temperature during impregnation within the range of about C., and said solution of nitric acid having a temperature during impregnation and prior to said exothermic reaction of about 45 C.; and then (D) controlling the temperature of the raw material during the reaction so that it does not exceed about 97 C.

References Cited UNITED STATES PATENTS 1,805,799 5/1931 Benson 162-90 2,539,093 1/1951 Mainguet 16281 X 2,597,430 5/1952 Baudiniere 162-81 3,130,115 4/1964 Thomsen 162-81 X FOREIGN PATENTS ADl871-605 3/ 1871 Great Britain.

S. LEON BASHORE, Primary Examiner R. D. BAJEFSKY, Assistant Examiner US. Cl. X.R. 162-90 

